Demolition hammers are used on work sites to break up objects such as rocks, concrete, asphalt, frozen ground, or other hard objects. The hammers may be mounted to machines, such as back hoes and excavators, or may be hand-held. The hammers may be powered by a hydraulic or pneumatic pressure source. In operation, a high pressure fluid drives a piston to strike a tool bit, which in turn, strikes rock, concrete, asphalt or other hard object to be broken up.
Lubrication systems are used to supply lubricant, such as grease, to bearing surfaces in the hammer to reduce friction between moving parts, such as between the tool bit and bushings that are used to align the tool bit. The lubrication system may be separate from the hammer, for example by being mounted on a carrier machine, or mounted to the hammer, i.e. an on-board system. Whether externally mounted or on-board, a lubricant supply is provided with the system. Operating the hammers without lubrication can result in significant damage to the hammer. In order to monitor the amount of lubricant remaining, many systems provide inspection windows, so that an operator can visually monitor the amount of lubricant remaining. Such systems, however, are dependent on the operator taking the necessary steps to manually check the window.
The system in U.S. Pat. No. 5,060,761, to Arndt, et al., discloses a lubrication system that uses a limit switch in the lubricant reservoir. When the lubricant level approaches a predetermined limit position, a horn and a warning lamp are activated to alert an operator to a low lubricant level. In addition, the limit switch can also be used to provide a signal to a control valve, which in turn actuates a turn-off valve that interrupts the operating pressure to the hammer, thus shutting off the hammer when the lubricant level has reached the predetermined limit position.
While the '761 patent provides a low lubricant warning and shutdown feature, it requires multiple additional components to activate, such as a limit switch, a control valve, a shut-off valve, and a power source to actuate the control valve.